Fan blade and its formation



Jan.8, 1952 w. E. MORRISON 2,581,873

' FAN BLADE AND ITS FORMATION Filed Dec. 17, 1947 I NVENTL'OR; WILLIAME. MORRISON Patented Jan. 8, 1952 UNIT ED STATES G 'FF I 7 "$581,873 1FAN' BL'ADEFAISD ITS'EOBMATIQN 'Wil1iam"E.Morrison, iTorrington,Connyassignor toTheTorringtonManufactmingfibg Torrington, Cnn.,'-a*corporation of Connecticut v- Applicationl-December 17, 1947,Senial 'No..7;9 2,130

invention relatesstoj fan" bladesarid, their .formation, and moreparticularly to eertainim- .provemeni'ls in both 7 the sectional shaping.and plan, contour of the bladesof' propeller typ'ej'fans,

the,.,im provements' being ideally adapted to 7 fans "for relatively.highuair delivery or volume within relativelylow pressure ranges, .suchas soecalleid -atticians. The present improvements are, however, broadly.a'daptedj'for ,use'in numerouslinstallations requiiinglbw,pressure;high volume air propellers. V

'Ihe ,greatlyj increasedrextent of .use of flarge .diameter ,propellersfor ventilation Y purposes generally,and particularly in the vfield of.so-

called atticxf ans; has .directe'dmuch. experimental work to the end ofproviding .a more quiet and efficient type .of; fan for this purpose.vMany, .of the ,air,propell'ers heretoforeoffered to thetrade exhibitall lower efficiency in; this field of usage, than should beexpec.tednin view vof experience wfix-ith V othfit propellers; in a.variety of other ,flelds. The presentinventionaccordingly has asamaiorobject, 'the improvement .of efliciency, of'jans-"for 'the' generalpurposes noted,,at1the same time realizing a more quiet, propeller.

7 Somewhat more particularlylstated, lthcpre'sent' improvements,objectively realize. a. more er,- iicientffan Lforilow pressure,i highvolume work, by application of what'is herein fde'signatedgas .theinductiongprinciple hereinafter ,more .Zfiilly explained, V

illn'iurltheranceof the obi elct', last above .expresse ed, additionalimportant ,objectivelfeatures of the .designincludelthe use of arelativelysmalllcenter fdiscl or spider. for the purpose ,of blade.mount ing; a design to, permit .a maximum, bladeengle, conducinjg" tolarge i open, passages of great area between the blades, and .a jrelatively vnarrow blade ,roo'ti'pa'rtion, further conducingtolaisubstantial-section of air channel betweentheadjacentIbladerootyportions; inikeepina withijthe 'in'ducti'onitheory above noted.

A1 further and" highly importantaobjectwof the ,present improvementsisattained in animprove'd .bla'derfbrmation such that a propellerff'ormed16f 'ithese' blades willexliibitahigh mefchanieal.efli-v ciency in the"low pressuregrange. of; its performance curve.

The "foregoing fan'drnumerous lothen objects will more clearlyappear'jsfromlthe" fbllowingide- Claims. (01.1'170-1-159) tailed(descriptions of a; single; preferred. embofii- 'ment' ofilthe inventionas lappliedetona propeller fan"for use". invarious.ventilation-."fielda. forwexamplewasl, in .an attic; tan,of,,,36 "-.cliameter, the description .1heing. predicated .l on we gramof n. this size, and'ltype, andbest understood'iuwhen loonsi'deredllnconnection with the. accompanyingidraw- .ingr in which:

' Fig.. 11 is ,a plan view o'fithe' pressure ,or delivery facevoffltheimprovedpropellerifan and center disc, only two blaclesv beingshowniorlclearness, vone thereof being broken away;

Figi'zis .a'front, elevation of a'i:four""biade;fan with presentimprovements, being thegmost usual embodiment;

i Fig? 3"is a planview of, a" blade blank,;,with'the view takenofi'thejpressureface of" the blad'ei'after blanking,..butibeforejforming; henoej'in unpitched V relation;

"Rig; '4 11s a fragmentary section the location of which;ina'forrned'lblade, is. alone 1ine?4 4.;of -'73)- F;ig;.1'5 "is affurther 1 section, "and" being fragmentary nature,ifthisi'section"'being' located,

Fig. 6 is a fragmentary "sectional view, the

location of which in aiormedbladeglisindicated fFigf "l is a transversesection taken on-a' curved 1 plane; parallel to" but-somewhat'inwardlrof the peripheral edge of the'blade; the location-there'- ofbeingli'designatedi'by line Y 1 11 of 1', this If gure including, inclotted ;lines,y"an' edgevportion of .the center disc "in ordertto"portray, 'iiiat- -grammatically;"the pitch of" the blade;

Referring 'now by characters "of"re'ference "to the "drawin thepropellerifan' is comprised of a selected, small plurality of blades.formed ofgza suitable sheet, material, ,such as, "sheet steel "oraluminum, "the blades being attached at equiiangular "intervalstoandgabout a" spider :of any suitable "form, exemplified in the present(dis- Jc'losure ,as ,a ,planar, center disc' 1,0. iThelblades aremountedlto provide a pitch angle oflitheprtier of i5ffdegrees lin theexample shown. The disc 10 j,isc-ap.ertured, at III .ffor a. .hub .Lor:..dther' suitable. shaft lmounting element j (notalshownl'l. ,Thenumber, of bl'a'deslis: oicourse optionalmthere .usually; being two,'ithree, or ;-four in avian-of, the

general ttype illustrated ;.and for the. fields ofincluded herein sinceit constitutes per se, the subject of a copending application Serial No.711,273, filed November 21, 1946, by this applicant. It may be noted,however, that the tabs l3 and I4 are bent along lines 2| and 22 so thatthe body of each tab lies outwardly from and at a distinct angle to theface or faces of the center disc; and each tab forms therewith, a shorttubular passage 23 adjacent the center disc and directed toward themedial region of the root portion of the blade.

Proceeding now to a description of the nature, contour and formation ofthe body of the blade til proper, it should be noted that the apparentdifference in blade width between Figs. 1 and 3, is due to therelatively high pitch preferably imparted to the blade in mounting sameon the center disc, and derived by the angularity and leading edge 24,through a rounded corner 25,

which would otherwise appear as an apex, merges into a widely arcuatelyformed peripheral margin 26' which is or ,may be of substantiallyregular curvature although possibly deviating to a very minor extentfrom a regular curve. The line or edge 26 is brought inwardly in arounded corner 2'1, thence merging into the trailing margin or edge 30of the blade. The edge 30 is approximately radial and is shown as beingstraight.

CItiwill appear that if the lines 30 and 24 were to be continuedinwardly they would intersect in or near-the axis of revolution, orperhaps slightly outwardly thereof. It will be obvious to those involvedwith the design of propeller blades that the rounded cornering 25 and21, as is of itself well known, conduces to quietness of operation.,Butfor such elimination of true apices, the blade in plan wouldgenerally resemble a triangle modified by rounding of one side such as24, shown asbeing a uniformly curved line on a radius of 14 inches, andthe base such as 26. If the blade be considered as an uppermost blade,such triangle-or quasi-triangle would be viewed in inverted'frelation,and by reason of the root portion should be considered as furthermodified in that itis' frustrate in what becomes the root portion of theblade. This shaping, as will appear from the drawing, results in anunusually narrow root -portion which conduces to the provision of amaximum path of air ingress in the regions of the blade roots, and overthe periphery of the center, disc, The proportions of the blade asviewedflin' plan or outline, are further such that the blade width in orjust inwardly of its pe ripher preferably substantially equals or evenexceeds the length of its active surface on a radius drawn from thecenter of revolution. Thus the fan is of a distinctly wide blade type. i

Over considerably thegreater part of the area of its pressure or forwardface each fan blade is of nearly flat, or of concave aspect, with theexception of a minor portion hereinafter noted in the trailing area ofthe blade. For consideration of blade formation, specifically itsvarious sectional shapes, it may be considered as divided into threeareas as viewed on its pressure or forward face. Thedirection ofrotation is indicated by the large arrow near the periphery of thecomplete blade of Fig. 1. Thus the curved leading margin 24 togetherwith a part of the peripheral edge 26 and a forming line AB, bounds aquasi-triangular leading area A-25-B. The line AB, located at an angleof 20 degrees to a radius through point B, may be considered as themedian of a channel directed from the root region near point A outwardlyto the periphery of the blade at B. On the leading side of the line AB,the pressure face of the fan is concave on forwardly projecting radii,and on the trailing side of line AB, as will be described, there is alarge practically flat area ABC, which may be very slightly curved onvery large forward radii. In the area of which line AB is a trailingboundary line, there is a forming curvature on forward radii, theseradii being approximately, but without restriction, of the order offourteen inches. Thus the area A-25-B constitutes a portion of the wallof a cylinder of that radius, and merges gradually and smoothly into thearea ABC. This formation results in a channel on the forward face of theblade which slopes in the direction of air flow as will appear, from theblade root about point A, and thence extends toward the peripheralregion in the general direction of air movement across the blade whenthe fan is in motion.

In the preferred construction as shown, a second preferably rectilinearforming line is indicated at CB, located at 16 degrees to the radiusthrough point B, the lines AB and CB being of converging trend towardthe periphery of the blade, as will be noted. The generally triangularspace between forming lines AB and CB constitutes an intermediate,approximately fiat triangular area or zone. The formation curvature ofthe area just beyond line CB, is preferably, for best results, in atypical fan blade of 36" diam eter, on forwardly projected radii of theorder of ten inches. Thus it will now appear that the area bounded byBCD constitutes a portion of a cylinder having a radius of ten inches,and that the area ABC merges smoothly and gradually into BCD. This partcylindrical formation constitutes a channel from the region of point Cto the periphery, and which slopes opposite the general direction of airmovement across the blade when in motion.

The third forming line CD which is somewhat shorter, by reason of itslocation, than the two described, lies at an angle preferably of theorder of 30 degrees to the line CB, and bounds a channel presentedon theback or intake face of the blade, resulting in a similar convexitypresented on the pressure face of the fan. The relation between the teninch positive curvature of area BCD, and the last noted negativecurvature characterizing the area D-2'l-C on backward radii, bestappears from the section of Fig. 6. The backward radii on which thelatter area is formed, are preferably of the order of six inches. Thusthe area D-Z'I-C constitutes a portion of a cylinder of this radius. Itwill now have appeared that the several groups of forward and backwardradii, as described, may be considered as ranged parallel to the forminglines, with those of each group considered as being in a row tangent toa circle on the axis of propeller revolution.

It will now have appeared that the concave region bounded by lines CBand CD consists of a relatively inverted triangular area which may beconsidered a trailing portion of the blade, and that the line CD takenwith the trailing extremity of peripheral edge 26, and trailing edge30'.

trail n :directionirom.theileadin dger-24- h are: 1 ;F gz .1 to takeiraranexamp e f aicircular-arceconce iawith h xis; of: rota: tion. Fi beina;,..section l view: takenalon the..said.arc-;.. By. ref en e Q a; '7 tw ll b ob: served: that thepitch: n les a e p o e s greater-at thefollowingfiones; spacedin the'traile 'ing directionz the;zoneimmediately'yadjacentthe leading. ed e; the-zone midw y t een-t leadingedge. 24.1.and1the line BA, the zone betweenthelinesBA andBC, the zonemidway betweenthe linesBC andDQ, ndtheizone immediately adjacent and 1.at; the leading; side of the D9,, Thepitchanglessimilarly'increaseprogres: sivelyrxalong: each otherarcconcentricwith the axis; rotation and-.beyondor spaced. outwardlyfrom the root areas From the foregoing description it will beobservedthatthe forwardly curved leading area 3.2! of thebladeispreferably a cylindrical section which is tangent alongthe line AB tothe central area 32. The line AB intersects a radial line through thecenter of the blade at a substantial angle with its outer. end at theperiphery and with its inner end'at the leading edge. The forwardlycurved area 33 of the blade is preferably a cylindrical section which istangent along the line CB to the central area 32. The line CBintersectsthesaidradial line through the center of the blade at anopposite substantial angle with its outer end at-t-he periphery and withits-inner endat the trailing edge.- The central area 32 is preferablytriangular and is also preferably flat orsubstantially flat.

When themain portion of the blade is formed with two cylindricalsections such as 3| and 33 which are tangent to an intermediate flatsectionsuch asr,32 narrower at the periphery than atthe, root, theconcavity of the mainportion isidifierent along difierent arcuate linesconcentric with the axis of rotation. The extent of concavity decreasesprogressively from the peripherytothe-root region. For instance, aconcentric arcuateline near the periphery intersects only ayery narrow.portion of the flat area 32 andthe, degree of concavity is substantiaL,A concentric arcuate line substantially nearer the center intersects amuch wider portion of the fiat area .32 and the degree of concavityalong the last said line is.considerably less. A concentric arcuate linethrough the points A and C intersectsonly the flat area 32 and there isno concavity.

The rearward curved trailing portion 34 joins the forward curved area 33alongthe forming orpjuncture-line CD. The outer end of the said line atD is substantially spaced in the trailing directionjrom a radial linethrough the center of; the blade, that from-a radialline throughthe-poin B... The line, extends.,-eenera11y inward iromthenointfl and"the :inner end ofthelineeat C:is located; at the. trailing-i edge: and'isi-substan; tiallyspaced; from the blade periphery. Then .1tion:3.4.sis.bo.unded;in partby an arc such:-as;-2] which is tangent .tothe arcuate peripheral-ledge 26- and is also tangent to theradialtrailingiedge 30;

The particular 'blade formation as; described has resultedfrominnumerable experiments; fole lowed .by-and including usualdeterm-inationsaof air stream-movements, as by: smoke streams.:andstroboscopic observation, and. it may. bezhere noted that the efiiciencyof the fan in compari-.-- son with a uniformly concave blade, is-materially increased by addition of 'thechannelling of the area 3|.Similarly,- advantages are ofiered' by the channelling characterizingthe area 33;-however, a greatly improved performance is-noted upon theintroduction ofboth'of these features of formation, and still further bythe reversely curved trailing lip-34 resulting from the backward radiias described, the latter particularly'serving to minimize, infact-virtually to prevent ina moderate'speed fan; the-adverse effectsometim'esvdescribed as a-tip-vo-rtexor-eddy.- I

In presenting applicantstheory-as -to opera.- tion of a fanconstructedand formed asrdescribed; it should first-bencted that-the -designthroughout is predicated upon what isherein for brevity-and aptness,referred to as the "air induction principle. Fundamental *in thistheoryof operation is theuseof acenter'discor-spider of a relatively small-area, h ence if'circulaizof a diameter which bears'a low proportiontothe diameter-of the fancircle. It hasbeen proven'as a result ofapplicants experiments that a propeller-with a minimumcenterobstruction-exhibits a relatively higher mechanical efliciency atlow delivery pressures than comparable pro: pellers with larger centerdiscs or the like, Further, the provision, one example of which has beenheretofore, described, of a maximum practical open area around the hubregion, has. been shown to give a high mechanical efiicienc'y throughthe low pressure range of the perform: ance curve of the propeller. Thisrange ashore: tofore implied,"is1th'at over which ventilatingand attic,fans willusually operate. Applicantsb: lief as .to thereasonsjor orexplanation, oimthe high efficiency attained at low pressures is thatthe high-velocity tubular or annular tream emanating fromapproximatelyLthe outer onee thirdgof thefagbla'des, resultsinapressure. drop or cavitation which effect is believed towbe-greattgestionthefrontzcenter ofthe fan. Itnow follows that, assuming the rootregions of the blades-to. be mutually well spaced, and thecenter ofr-thewhole propeller of relatively open design the higher pressureairon theintakeiside of theifan will be'induced ordrawn through such open areainto the, low pressure ,zone centrally of thepressure face, andwillthereupon augment the volume, of'air positively im filled by the fastermoving outer part, of the propeller. It is applicantsizbee. lief thatsuch portion of. the air delivery,.,namee ly, that part whichisinduced-by "flow into and about 1 its center region, is attained with;virtually little. increasein power requirement, inasmuch as the'energynecessary forsuchinductiomhas theretofore ibeenexpended in thedevelopment of the, ;velocity of j the stream impelled by -the. outer.-most one-third (for example) of the-fan circle. It is felt thatthistheory accounts for the rise -in' mechanical. efficiency oi thepropeller; It -is iii keeping with this principle that the center disc Iis kept small, and blade angle is preferably at a maximum to providegreatest open area between the blades, which effect is further.augmented by minimizing the width of the blade root regions.

The Wide divergence between lateral blade margins conduces to a high airvelocity in the peripheral region, at the same time obstructing no morethan necessary, the induced central stream of air. The extremedivergence of leading. and trailingmargins presents the advantages ofwide-blade fans, including quietness of operation.

, By way of. explanation of the advantages of the general formation ofthe blade as to its varying concavity and location of forming lines, itmay be noted that the relatively large forward radii characterizing, thearea 3|, give the effect of a substantially constant pitch to theleading area of the'blade, and thus minimize drag losses on the outerportion thereof. Further, such forming results in the channelled sectionextending outwardly of the axis in the direction of rotation,thischannelbeing of material aid in imparting a centrifugal effect tothe induced air entering the blade, causing it definitely to rise on theblade. Such outward component of air motion persists until its'radialforce component is neutralized by the atmospheric pressure about theblade periphery, acting to impel the air into the low pressure zonecreated by axial velocity of the de scribed tubular air stream.

As heretofore briefly noted, the channel beyond the forming line CB,being in area 33, and on a somewhat lesser radius than the leading area3|, provides additional axial velocity to the flow resulting from theactual air contact with the blade. This channel is sloped oppositely tothat of area 3|, and thus imparts a centripetal effect to the air,somewhat compensating the centrifugal action of area 3|, and coacts withthe air pressure about the periphery in forming and maintaining thetubular character of the fan stream. 1

The backwardly formed trailing area is an added feature of design forbest results, and permits'a smooth takeoff of the positively axiallyimpelled air stream, and prevents all but a negli gible minimum ofturbulence loss or tip vortex,

otherwise resulting in the recognized blade tip r drag.

Tests indicate'that the outer diameter of the annular or tubularvelocity ring is substantially the same as the fan diameter, since theeffect of ambient air pressure thereabout, serves thus to limit theouter diameter of this high velocity cylinder. Theinduction theoryheretofore described is upheld by the shape and pattern of theeificiency curve-of propellers constructed substantiall as described;such curve shows the highest efiiciency in the region of zero staticpressure and decreases only very little as static pressure is slightlyincreased, then diminishes rapidly with successive-increases in staticpressure. It is not intended that a propeller designed as described willexhibit high efficiency against high pressures, this being inherentlyinconsistent with the theory of a centrally induced flow, it beingpossible to attain such flow only within a low range ofworkingpressures. It will, however, appear that a fan designed inkeeping with the theory discussed, will realize the many advantages ofpropellers characterized by, wide blades with ofi-i radial channelling,and will serve fully to attain each of the several'objects hereinaboveexpressly stated and others implied from the structural description of aselected exemplary embodiment.

Although the invention has been described by specific reference to asingle propeller of commercial type, the specification should not beunderstood in any limiting sense, inasmuch as numerous variants arepossible within thescope of the appended claims. 7

I claim as my invention:

1. The combination in a fan, of a rotatable hub and a plurality ofsimilar blades securedthereto at substantial pitch angles each of whichblades is of uniform thickness, the main portion of each blade beyondthe root area thereof being generally concave at the pressure or forwardside thereof and the leading and trailing areas of the said main portionbeyond the said root area being forwardly curved sections tangent to aplane having a substantial pitch angle, thesaid leading forwardly curvedsection being tangent tothe said plane along a line which intersects aradial line through the center of the blade at a substantial angle withits outer end at the periphery and with its inner end at the leadingedge of the blade and the said trailing forwardly curved section beintangent to the saidplane along a line which intersects the said radialline at a substantial angle with its outer' end at the periphery andwith its inner end terminating at the trailing edge of the blade.

2. The combination in a fan, of a rotatable hub and a plurality ofsimilar blades secured thereto at substantial pitch angles each of whichblades is of uniform thickness, the main portion of each-blade includinga substantially'fiat triangular central section located at a substantialpitch angle and having'its base at the root area of the blade andthesaid main portion of the blade also including two cylindrical sectionsat the leading and trailing sides of the triangular central section,which cylindrical sections are curved in the pressure 01' forward direc;tion, the said leading cylindrical section being tangent to the saidcentral section along the leading edge thereof and the said trailingcylindrical section being tangent to the said central section along thetrailing edge thereof.

3. The combination in'a fan, of a rotatable hub and a plurality ofsimilar blades secured thereto at substantial pitch angles each of whichblades is of uniform thickness'and has an arcuate peripheral edgesubstantially concentric with the axis of rotation, each bladecomp-rising a main portion and also comp-rising a. trailing portionwhich is curved in the intake or rearward direction, the 'said'mainpo'rtion of each blade beyond the root area thereof being generallyconcave at the forward'side and the leading and trailing areas of thesaid main portion beyond the root area being forwardly curvedsubstantially cylindrical sections tangent to a plane having asubstantial pitch angle, the said leading cylindrical section beingtangent to the said plane along a line which intersects a radial linethrough the center of the blade at a substantial angle with its outerend at the periphery and with its inner end at the leading edge of theblade and the said trailing cylindrical section being tangent to thesaid plane along a line which intersects the said radial line at asubstantial angle with its outer end at the periphery and with its innerend at thetrailing edge of the blade, and the said rearward curvedtrailing portion of each blade joining the said main portion along asubstantially straight juncture line which extends generally inward froman intersection point located at the said peripheral edge of the bladeand substantially spaced in the trailing direction from a radial linethrough the center of the blade and which terminates at a secondintersection point located at tile said trailing edge of the blade andsubstantially spaced from the blade periphery.

4. Thecombination in a fan, of a rotatable hub and a plurality ofsimilar blades secured thereto at substantial pitch angles each of whichblades is of uniform thickness and has an arouate peripheral edgesubstantially concentric with the axis of rotation, each bladecomprising a main portion and also comprising a trailing portion curvedin the intake or rearwarddirection and bounded in part by an arc ofsubstantially uniform convex curvature tangent to the saidarcuate-peripheral edge and also tangent to the trailing; edge of theblade, the said rearward curved trailing portion of each, blade joiningthe said main portion along a substantially straight juncture line whichextends generally inward from an intersection point located at the saidperipheral edge of the blade and substantially spaced in the trailingdirection from a radial line through the center of the. blade "and whichterminates at a second intersection point locatedat the trailing edge ofthe blade and substantially spaced from the blade periphery.

5. The combination in a fan, of a rotatable hub and a plurality ofsimilar blades secured thereto at substantial pitch angles each of whichblades is of uniform thickness and has an arm-- ate peripheral edgesubstantially concentric with the axis of rotation, each bladecomprising a main portion which is concave at the pressure or forwardside thereof and also comprising a rearward curved trailing portion, thesaid main portion of each blade beyond the root area thereof being soformed that the pitch angles along each circular arc concentric with theaxis of rotation progressively increase in the trailing 10 directionfrom the leading edge thereof to the said trailing portion and, the saidmain portion beyond the root area thereofbeing also so formed that itsconcavity along suc'cessive circular arcs concentric with the axisfofrotation progressively increases from the said' 'oot area to theperiphery, and the said rearigvard curved trailing portion of each bladejoining the said main portion along a substantially-straight junctureline which extends generally; inward from an intersection point locatedat the said peripheral edge of the blade and substantially spaced in thetrailing direction from'i'a' radial line through the center of thebladeand which terminates at a second intersection jjpoint located atthe said trailing edge of the blade and substantially spaced from theblade periphery.

WILLIAM E. MORRISON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UN ITED STATES PATENTS Number Name Date 328,549 Viggers Oct. 20, 1885505,902 Leslie Oct. 3, 1893 1,370,284 Carlson Mar. 1, 1921 1,506,947Miller Sept. 2, 1924 1,508,086 Crawford Sept. 9, 1924 1,688,462 OswaldMay 1, 1928 1,806,345 Halvorsen May 19, 1931 2,023,111 Alsing Dec. 3,1935 2,031,466 C'riqui Feb. 18, 1936 2,056,547 Weber Oct. 6, 19362,148,555 Hicks Feb. 28, 1939 2,212,041 Pfautch Aug. 20, 1940 2,370,652Frisbie Mar. 6, 1945 2,390,804 McLean Dec. 11, 1945 FOREIGN PATENTSNumber Country Date 485,041 Great Britain May 13, 1939

